\chapter{Experiments and Results}
\label{ch:experiments}
This chapter explains the three different setups that we have used for the experiments. Details on RSSI and LQI evaluation vs. distance will be provided and discussed.

\section{Setup 1: IHA corridor}\label{sec:setup1}

\subsection{Scenario}
The first experiment was carried out at the Engineering College of Aarhus (IHA) in the first floor corridor. In this setup there was a clear line of sight (LOS) between the base station and the remote node. The base station was fixed, so the position of the base station TelosB was constant. In a similar way, the remote node was placed on a trash can. This kept the node in the exact same horizontal position relative to the moving surface. The antenna orientation was kept constant. The exact scenario for the experiment can be seen in figure~\ref{fig:corridorScenario}. The concrete base station and mobile node setup can be seen in figure~\ref{fig:corridorSetup}.

\subsection{Data collection and results}
Following the methods explained in the previous chapter, 20 readings of RSSI and LQI values were recorded every 2 meters. After logging the values, they were processed and plotted, achieving the results shown in figures~\ref{fig:corridorRSSI} and~\ref{fig:corridorLQI} for RSSI and LQI cases respectively.
Note that some of the readings are overlapping, therefore at some points there are less than 20 RSSI readings shown.

As it can be seen in figure~\ref{fig:corridorRSSI}, the RSSI drops constantly until a distance of 20 meters. Between 20 and 50 meters, the RSSI starts to oscillate around -70 dBm. As shown in figure~\ref{fig:corridorLQI} the LQI values are even more erratic. There is a significant drop at a distance of 30 meters from the base station, that is compensated when the mobile node reaches 40 meters. All in all, the LQI values retrieved in this 50 meters range can be considered very good, since they do not go below 102 in average.

The obtained data drifts from the expected values according to the Path Loss propagation model (see equation~\ref{eqn:pathLoss}). There are a number of reasons that explain these results:
\begin{itemize}
\item Heavy traffic in the 2.4Ghz band: access points at the corridor have an RSSI of -50 dBm. 
\item Reflections: the corridor is the perfect environment for signal reflections. These reflections start to be a problem when the remote node start to be far from the base station (in this case 20 meters).
\end{itemize}

Still it was possible to adjust the path loss propagation expression to model partially the signal evolution. In figure~\ref{fig:corridorRSSI}, the blue curve  corresponds to the path loss model, with the values $n=2.0$ and $A=45$.

\begin{figure}[!ht]
  \centering
  \includegraphics[width=0.9\textwidth]{figures/indoor1.jpg}
  \caption{Base station connected to a MAC and mobile node on top of the trash can. In this case the system is evaluating RSSI and LQI at a distance of 1 meter.}
  \label{fig:corridorSetup}
\end{figure}

\begin{figure}[!ht]
 \centering
  \includegraphics[width=0.9\textwidth]{figures/indoor2.jpg}
  \caption{Environment in which the first experiment was carried out. Base station in the first plane and mobile node 10 meters away.}
  \label{fig:corridorScenario}
\end{figure}

\begin{figure}[!ht]
  \centering
  %\includegraphics[width=0.9\textwidth]{figures/corridor-rssiimg.png}
%\includegraphics[width=23cm,angle=90]{figures/rssiIndoor.png}
  \includegraphics[trim = 19mm 19mm 19mm 19mm, width=23cm,angle=90]{chart_rssi_indoor.pdf}
  \caption{RSSI vs. Distance in experiment 1.}
  \label{fig:corridorRSSI}
\end{figure}

\begin{figure}[!ht]
  \centering
  \includegraphics[width=0.9\textwidth]{figures/corridor-lqiimg.png}
  \caption{LQI vs. Distance in experiment 1.}
  \label{fig:corridorLQI}
\end{figure}

\section{Setup 2: Open space}\label{section:openSpace}

\subsection{Scenario}
The second experiment was carried out in the football yard close to IHA. This scenario was specially good for the experiment since it presents the following characteristic:
\begin{itemize}
\item LOS up to 180 meters
\item Surrounding WiFi RSSI values of -90dbm: This reduced the interferences between the WiFi signals and the 802.15.4 signals (both of them operating in the 2.4 GHz ISM\footnote{Industrial Scientific Medical: acronym to refer to certain bands that do not required specific license to be used. These bands vary depending on the ITU-R region (International Telecommunication Union Radiocommunication Sector} band).
\end{itemize}

The base station was lifted using a trash can, and remained at a fixed position during the whole experiment. This ensured that the antenna orientation was constant and pointing with the frontal layer to the remote node. This is relevant for the experiment since the antenna is not omnidirectional. The setup can be seen in figure~\ref{fig:BaseStation2}. The moving node was kept at a distant height of 1 meter, with the antenna layer orientated to the base station.

\subsection{Data collection and results}
The same methodology as in~\ref{sec:setup1} was applied, but in this case the measurements were carried out in the following intervals:
\begin{itemize}
\item 0 to 10 meters: 20 signal measurements every one meter.
\item 10 to 60 meters: 20 signal measurements every 5 meters.
\item 60 to 100 meters: 20 signal measurements every 10 meters.
\end{itemize}

These data offer the maximum resolution in the 0 to 10 meters range, while still keeping a good characterization of the signal decay in the two following intervals. The collected data was plotted and the results are shown in figure~\ref{fig:rssiOutdoors}. The averaged data can be seen together with the expected results from the path loss propagation model. The blue curve corresponds to the propagation model, by using the parameters $n=2.3$ and $A=48$. Special mention requires the RSSI and LQI value oscillation between the 25-35 meters interval. 


The LQI evolution, as in the rest of the experiments, is unpredictable. It starts with a value of 105 for the first 10 meters, and it stays below 80 from 60 meters to 100 meters. In the section in between, the value tend to oscillate. During the latter interval there was a considerable number of packet retransmissions, and it took a long time to receive the 20 packets required for the experiment.

\begin{figure}[!ht]
  \centering
  \includegraphics[width=0.9\textwidth]{figures/outdoors1.jpg}
  \caption{Experiment 2 environment. The experiment was carried out in a football yard with perfect LOS, as it can be seen in the picture.}
  \label{fig:test}
\end{figure}

\begin{figure}[!ht]
  \centering
  \includegraphics[width=0.9\textwidth]{figures/outdoors2.jpg}
  \caption{Base station used for the outdoors setup. The pc was lifted with a trash can and the telosB antenna was facing the remote node.}
  \label{fig:BaseStation2}
\end{figure}



\begin{figure}[!ht]
%  \centering
  %\includegraphics[width=0.9\textwidth]{figures/openspace-rssiimg.png}
  \includegraphics[trim = 19mm 19mm 19mm 19mm, width=23cm,angle=90]{chart_rssi_open_space.pdf}
%\includegraphics[width=23cm,angle=90]{figures/rssiOutdoor.png}
  \caption{RSSI vs. Distance in experiment 2.}
  \label{fig:rssiOutdoors}
\end{figure}

\begin{figure}[!ht]
  \centering
  \includegraphics[width=0.9\textwidth]{figures/openspace-lqiimg.png}
  \caption{LQI vs. Distance in experiment 2.}
  \label{fig:lqiCorridor}
\end{figure}

\section{Setup 3: Radio dead room (telosb)}\label{sec:setup3}

\subsection{Scenario}
This experiment was carried out in the radio dead room at IHA. The advantage of this room is that it is able to attenuate (to some extent) the radio signals. The purpose of carrying out the experiment in this scenario is to avoid possible interferences. The base station is connected to the PC and with the antenna facing the mobile mote, as explained in~\ref{section:openSpace}.

\subsection{Data collection and results}\label{sec:deadRoom}
Due to the small dimensions of the radio dead room, the values were taken from 0 to 4 meters. in intervals of 1 meter. The obtained results can be seen in the plot shown in figure~\ref{fig:rssiDeadTelosb}. As shown in the averaged data, the signal is oscillating between -40 and -60 dBm. These results are not presenting the logarithmic decay expected from the propagation model.
 
\subsection{Improvements to the experiment}
In order to obtain more meaningful results, the transmission platform of the base station could be lowered.

\begin{figure}[htp]
  \centering
  \includegraphics[width=0.9\textwidth]{figures/radioDead1.jpg}
  \caption{Running the experiments in the radio dead room. Base station on the left and mobile node on the table.}
  \label{fig:test}
\end{figure}

\begin{figure}[htp]
  \centering
  \includegraphics[width=0.9\textwidth]{figures/radioDead2.jpg}
  \caption{Detail of the base station placed in the radio dead room.}
  \label{fig:test}
\end{figure}


\begin{figure}[htp]
  \centering
  \includegraphics[width=0.9\textwidth]{figures/radiodead_telosb-rssiimg.png}
  \caption{RSSI vs. Distance in experiment 3 with the TelosB motes.}
  \label{fig:rssiDeadTelosb}
\end{figure}

\begin{figure}[htp]
  \centering
  \includegraphics[width=0.9\textwidth]{figures/radiodead_telosb-lqiimg.png}
  \caption{LQI vs. Distance in experiment 3 with the TelosB motes.}
  \label{fig:test}
\end{figure}


\section{Setup 4: Radio dead room (ASEBAN)}

\subsection{Scenario}
The scenario used in this experiment is the same as the one explained in~\ref{sec:setup3}. 

\subsection{The ASEBAN device}

The ASEBAN mote has been developed at IHA as a small sensor mote to create a Body Area Network. The ASEBAN integrates a CC2420 radio transceiver, which is using the 802.15.4 protocol. This is the same transceiver as the one integrated in the TelosB motes. Since the protocol is the same, it is possible to receive frames transmitted from the ASEBAN in the TelosB.

\subsection{Data collection and results}
In this case the same setup as in~\ref{sec:deadRoom}. The results were considerable better than in the third experiment. The transmission power of the ASEBAN is lower than the one configured in the TelosB, therefore the signal decays at a lower distance. The results of this experiments can be seen in~\ref{fig:aseRSSI}. The LQI is maintained at a good level in average. In the plot shown in figure~\ref{fig:aseLQI}.

\begin{figure}[htp]
  \centering
  \includegraphics[width=0.9\textwidth]{figures/aseBand.jpg}
  \caption{A closer look to the ASEBAN mote.}
  \label{fig:test}
\end{figure}



\begin{figure}[htp]
  \centering
  \includegraphics[width=0.9\textwidth]{figures/radiodead_aseband-rssiimg.png}
  \caption{RSSI vs. Distance in experiment 3 with the ASEBAN mote.}
  \label{fig:aseRSSI}
\end{figure}

\begin{figure}[htp]
  \centering
  \includegraphics[width=0.9\textwidth]{figures/radiodead_aseband-lqiimg.png}
  \caption{LQI vs Distance in experiment 3 with the ASEBAN mote.}
  \label{fig:aseLQI}
\end{figure}
